A method and apparatus for setting a tank venting valve are known from U.S. Pat. No. 4,683,861. The method described there utilizes the lambda control factor which is supplied by a lambda controller function unit for controlling the lambda value of the air/fuel mixture to be supplied to the internal combustion engine. This factor is used for modifying values of a precontrol variable for a pulse duty factor for activating the tank venting valve. These values are stored in a memory addressable via the rotational speed and a load-dependent variable.
The known method works on the condition that essentially the same negative pressure continuously exists at the negative-pressure side of the tank venting valve, that is, at the opening of the tank vent into the air duct of the internal combustion engine. This assumes that the opening is located in front of the throttle flap. If, nevertheless, different negative pressures occur in dependence on different loads, this is taken into consideration by the fact that the values of the precontrol variable are stored in dependence on load. In the above-mentioned publication, however, it is expressly mentioned that greater pressure differences between different load conditions cannot be adequately taken into consideration.
Behind the throttle flap there is a much stronger negative pressure in the intake pipe than in front of it, especially when the flap is not completely opened. The consequence is that when the tank vent opens into the air duct, that is, into the intake pipe, behind the throttle flap instead of in front of it, much higher gas throughputs can be achieved with the cross sections of the tank venting lines remaining the same. Thus, the intermediate store, which as a rule is filled with active carbon, can be better and more quickly regenerated. The known method and the known apparatus, however, are not capable of satisfactorily controlling the fuel quantity to be supplied to the internal combustion engine in this case.
The invention is based on the object of specifying a method and an apparatus for setting a tank venting valve. The method and the apparatus also lead to good control results for the total quantity of fuel to be supplied to an internal combustion engine if the method and the apparatus are to be used in a system in which the tank vent is connected into the air duct of an internal combustion engine behind the throttle valve.